1. Field of the Invention
The present invention relates to a method of transforming a normally gaseous composition containing at least one hydrogen source, at least one oxygen source and at least one carbon source into a normally liquid fuel, furthermore the present invention relates to a normally liquid fuel and to an apparatus for transforming a normally gaseous composition into a normally liquid fuel.
One of the major problems facing mankind is the global warming of the atmosphere due to man-made emissions of greenhouse gases such as carbon dioxide, methane, chlorofluorocarbons, nitrous oxide or ozone. One possible approach to mitigate the emissions of these greenhouse gases to the atmosphere would be to recycle them in a chemical process to form useful products. Among all the man-made greenhouse gases, methane and carbon dioxide contribute to most of the greenhouse effect.
2. Description of Related Art
Intensive investigations have been carried out either to convert methane into higher hydrocarbons by oxidative coupling of methane as well as to convert methane into methanol by partial oxidation of methane (reports of R. H. Crabtree et al. in Chem. Rev. 95 (1995) 987 and of H. D. Gesser, N. R. Hunter and C. B. Prakash in Chem. Rev. 85 (1985) 235; both reports being incorporated herein for all purposes by way of reference). However, the yield of objective products from these conventional catalytic methane conversions is too low for a practical application.
A great effort has also given to chemical fixation of carbon dioxide. Heterogeneous catalysis has been considered to be a desirable route for carbon dioxide utilization. But a large amount of additional energy or expensive hydrogen is required for conventional catalytic utilization of carbon dioxide since the carbon dioxide molecule has a very low energy content. There is still no confirmed technology by far for utilizing such a plentiful carbon source.
A few processes for the synthesis of liquid fuel starting from gaseous compositions are known, such as the xe2x80x9cMobil processxe2x80x9d and the xe2x80x9cFischer-Tropsch processxe2x80x9d schematically shown in equation (1) and (2).
CO+H2xe2x86x92CH3OHxe2x86x92gasolinexe2x80x83xe2x80x83(1)
CO+H2xe2x86x92gasolinexe2x80x83xe2x80x83(2)
For both heterogeneous catalyzed processes the production of xe2x80x9csynthesis gasxe2x80x9d, a mixture of CO and H2 also named xe2x80x9csyngasxe2x80x9d, represents the first step along the path to methanol and gasoline respectively. Even if the xe2x80x9cMobil processxe2x80x9d (eq. (1)) and the xe2x80x9cFischer-Tropsch processxe2x80x9d (eq. (2)) are practiced today for industrial fuel synthesis production, e.g in South Africa, Malaysia and New Zealand, they are non-economic xe2x80x9cpolitical processesxe2x80x9d, heavily supported by governmental subsidies. The lack of profitableness is either due to the usually required high pressures at which the processes take place as well as to the high production costs of syngas and the fact that the produced syngas needs to be compressed before applied in the processes (1) and (2). Thus, about 60% to 80% of the total cost of the processes (1) and (2) goes to production and compression of syngas.
The industrial production of syngas mostly derives from the energy-intensive steam reforming of methane shown in equation (3):
H2O+CH4xe2x86x92CO+3 H2 xcex94Hxc2x0=206.1 kJ/molxe2x80x83xe2x80x83(3)
Syngas can also be produced from the greenhouse gases methane and carbon dioxide as shown in equation (4). However, such a reforming of carbon dioxide by methane is also a very energy-intensive process and requires high temperatures. Moreover, deposition of carbon on the catalyst always causes problems for this reaction.
CO2+CH4xe2x86x922 CO+2 H2 xcex94Hxc2x0=258.9 kJ/molxe2x80x83xe2x80x83(4)
Non-equilibrium plasma chemical processes occuring in the volume part of electrical non-equilibrium discharges have attracted a great deal of interest. Particularly, silent gas discharges have demonstrated its suitability for large-scale industrial applications. The ozone generation, as its most important industrial application so far, is described by Eliasson et al. in IEEE Transactions on Plasma Science, Vol. 19 (1991), page 309-323 (this report being incorporated herein for all purposes by way of reference). It is to be noted that a characteristic of the silent discharge is the presence of a dielectric. Therefore silent gas discharges are also referred to as dielectric barrier discharges.
Recently, the utilization of greenhouse gases for the synthesis of methanol or methane in such silent gas discharge reactors has also been described. Thus, DE 42 20 865 describes a method and an apparatus for the hydrogenation of carbon dioxide leading in particular to methane or methanol by exposing a mixture of carbon dioxide and a substance containing hydrogen atoms, preferably hydrogen or water, to a dielectric barrier discharge. An overview of the progress in this field have been summarized by Eliasson et al. in Energy Conversion Management 38 (1997) 415 (this report being incorporated herein for all purposes by way of reference). It is noteworthy, however, that the reported maximum yield of methanol was only about 1%.
Accordingly, it is an object of the present invention to provide for a method of transforming a normally gaseous composition into a normally liquid fuel, which method can be carried out economically, preferably at low pressures.
It is another object of the present invention to provide for a method of producing liquid fuel from gaseous compositions in reasonable yields and in a direct manner, i.e. making the expensive formation of syngas no longer necessary.
Another object of the present invention is to provide for an apparatus that allows the transformation of a gaseous composition into a liquid fuel.
Further objects and advantages of the present invention will become apparent as this specification proceeds.
Accordingly, the invention provides for a method of transforming a normally gaseous composition containing at least one hydrogen source, at least one oxygen source and at least one carbon source into a normally liquid fuel, wherein the gaseous composition consists at least in part of carbon dioxide as the carbon source and the oxygen source, and of methane as the hydrogen source and as a second carbon source, which method comprises the steps of feeding the gaseous composition into a reactor that includes a first electrode means, a second electrode means and at least one layer of a normally solid dielectric material positioned between said first and said second electrode means, submitting the composition within the reactor to a dielectric barrier discharge in the presence of a normally solid catalyst, wherein said normally solid catalyst is a member selected from the group of zeolites, aluminophosphates, silicoaluminophosphates, metalloaluminophosphates and metal oxides containing OH groups, and controlling the dielectric barrier discharge to convert the gaseous composition into the normally liquid fuel. Typically, the normally solid catalyst is selected from the group commonly designated as shape-selective catalysts.
In a second general embodiment the invention provides for a normally liquid fuel obtainable by a dielectric barrier discharge, the normally liquid fuel comprising at least 60 mol % of hydrocarbons having a normal boiling range of between about 50xc2x0 C. and about 210xc2x0 C., and less than 10 mol % of oxygenated hydrocarbons.
In a third general embodiment the invention provides for an apparatus for transforming a normally gaseous composition containing at least one hydrogen source, at least one oxygen source and at least one carbon source into a normally liquid fuel as set forth in claim 9.